Impact of amorphization on the magnetic properties ofEuO-TiO2system

Abstract

Recently, we have reported amorphization-induced ferromagnetism in a magnetic oxide; whereas crystalline EuTiO 3 is an antiferromagnet, its amorphous counterpart shows a ferromagnetic transition. In this paper, we have investigated the magnetic properties of amorphous EuO-TiO 2 system in detail. The present compounds, i.e., amorphous EuTiO 3 and Eu 2 TiO 4 , exhibit a paramagnetic-ferromagnetic transition followed by a spin-glass transition upon cooling down, thereby being characterized as reentrant ferromagnets. Interestingly, the magnetic ordering temperatures of amorphous EuTiO 3 and Eu 2 TiO 4 are comparable to and higher than those of their crystalline counterparts, respectively, indicating the enhancement of ferromagnetic interactions by amorphization. The origin of these features is discussed in terms of both the essential structural difference between amorphous and crystalline oxides and the magnetism unique to the crystalline EuO-TiO 2 compounds. We also find a correlation between the magnitude of ferromagnetic interactions and the covalency of Eu-O bonds.

Local Structure of Amorphous EuO–TiO2 Thin Films Probed by X‐Ray Absorption Fine Structure

“…It has been known that when an insulating magnet transforms from crystalline to amorphous phase, the magnetic transition temperature is usually suppressed because of the magnetic frustration, which is caused by the predominance of antiferromagnetic interactions and the random distribution of the magnetic ions . Nonetheless, we have recently observed interesting magnetic properties in amorphous EuO–TiO 2 system, definitely different from those of amorphous insulating magnets reported so far . For example, the amorphization of EuTiO 3 results in a switching from the antiferromagnetic to ferromagnetic state, and the ferromagnetic transition is observed at T c =5.5 K, which is comparable to the Néel temperature of antiferromagnetic c‐ETO.…”

Ferromagnetic properties with reentrant spin‐glass behavior in amorphous EuZrO3 thin film

“…It has been reported theoretically and experimentally that the magnetic ground state of EuTiO 3 crystal is critically balanced between antiferromagnetic and ferromagnetic ones, and a transition from antiferromagnet to ferromagnet could be realized by a lattice expansion [6][7][8][9]. More interestingly, our recent study demonstrated that amorphization of EuTiO 3 results in a switch of the magnetic ground state from antiferromagnetic to ferromagnetic one accompanied with an increase in the Weiss temperature (θ W ) [10,11]. This result is contrary to the usual understanding that the magnetic transition temperature is suppressed by amorphization.…”

“…With decreasing T, an abrupt increase in M can be observed below 10 K, indicating a magnetic transition from paramagnetic to ferromagnetic phase. From the inflection point of M( T) curves, the ferromagnetic transition temperature (T C ) was estimated to be about 8 K, which is slightly higher than that of amorphous EuTiO 3 thin film [10,11]. As T is further lowered below T C , the M( T) curves for H dc = 20 and 50 Oe exhibit a discrepancy between those under ZFC and FC modes as shown in the inset of Fig.…”

“…3(b). In the high-T region the χ -containing oxide glasses [10,11,19], suggesting that the predominance of ferromagnetic interactions is intrinsic to amorphous oxides with high Eu spins can be easily flipped perpendicular to the applied magnetic field partly due to their small magnetic anisotropy, the hysteresis loop in the M(H) curve is difficult to observe clearly for such a system. We also measured M ac of amorphous EuZrO 3 thin film in order to further understand the magnetic interactions and phase transitions.…”

Magnetic properties of oxide glasses containing iron and rare-earth ions

“…1 Instead, short-range antiferromagnetic (AFM) superexchange interactions via 2p states of oxide ions are predominant in the magnetic oxide glasses, [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] with some exceptions such as Eu 2+ -containing glasses, where ferromagnetic (FM) interactions prevail. [19][20][21][22][23] In a system where magnetic moments are located at randomly distributed cations, the short-range AFM interactions inevitably bring about magnetic frustrations of geometrical origin. Consequently, SG phases appear at low temperatures due to the coexistence of randomness and frustration that are the key ingredients of SG.…”